Ancient Glaciers of New Zealand. 257 



above the level of the sea; and its bottom, therefore, is 400 

 feet lower than the surface of the ocean. On either side of 

 the lake, throughout its whole extent, the mountains rise 

 in a continuous series of very rugged peaks, to a height of 

 from 5,000 to 7,500 feet; while Mt. Earnslaw, which forms 

 the head of the valley, attains an elevation of 9,165 feet, its 

 top white with perpetual snow, and its sides scored by de- 

 scending glaciers. 



The valley of Lake Wakatipu extends southward beyond 

 the foot of the lake for a distance of fifty or sixty miles, and 

 opens out into the level country that forms the province of 

 Southland. As the physical features of the lower portion of 

 the valley are not essentially different from those of the im- 

 mediate shores of the lake, we are forced to consider them 

 as having a common origin, and being but portions of the 

 same valley; the upper part of which is filled with 1,400 

 feet of water, and the lower portion by an unknown depth 

 of worn and rounded shingle. The rocks that inclose the 

 valley are for the most part, clay-slates and gold-bearing 

 mica-schist, which are very much curved and twisted, and in 

 many places green with chlorite. 



We will not attempt to trace the geological history of the 

 mountains themselves, but will confine our attention to the 

 last chapter in their history — the formation of the valleys. 



Valleys may be considered as owing their origin, pri- 

 marily, to one of three causes. (1.) They are formed by a 

 folding of the rocks. These produce depressions, the sides 

 of which slope inwards towards the axis — synclinal valleys. 

 Examples of valleys formed in this way are to be met with 

 wherever stratified rocks have been upheaved, as in the 

 Sierra Nevada, Rocky, and Alleghany Mountains. (2.) 

 Valleys are sometimes formed by the fracturing of the earth's 

 crust by volcanic forces. Valleys of this kind are seldom 

 seen, being confined to regions of great igneous disturbance. 

 (3.) The kinds of valleys above noticed are usually greatly 

 modified by denudation, which is another great agent in their 



